In general, a mechanical system that is designed to provide a supporting and/or enclosing medium for an item of electronic equipment. The system may be equipped with supporting structures to carry standard-sized circuit boards in addition to a motherboard or backplane into which the boards are inserted and connected via sockets. Alternatively the individual components may be hardwired onto tag strips attached to the chassis.

For safety reasons the metal parts of most chassis are permanently connected to a local zero-voltage reference or ground. In some equipment, however, it is more convenient (but potentially dangerous) to connect the chassis to one side of the a.c. or d.c. line (mains) supply; the equipment is then said to have a hot (or live) chassis. The chassis may also be left unconnected or floating.